The field of the invention is optics, systems and elements having lens spacing structures with a dark field stage and the present invention is particularly concerned with an incident light illuminating instrument of modular design for light and dark field illumination.
The state of the art of incident light illumination instruments for selective light and dark field illumination may be ascertained by reference to U.S. Pat. No. 3,930,713, and this disclosure is incorporated herein to show the application to a microscope.
Incident light illuminators having fixed apertures and luminous field stops are known, which are preferably used for routine testing in the semiconductor industry. Furthermore, in research and development, there are incident light illuminators with iris apertures and luminous field stops as light-dark field devices for stringent requirements.
The prior art incident light illuminators, however, suffer from the drawback that for instance when passing from light field to dark field illumination, the user must carry out several manual operations, for instance opening the luminous field stop, adjusting the aperture stop and inserting the center stop. When one switches from the dark to the light field, these manual operations, which are time-consuming and prone to operator errors, must be carried out in the reverse order. Constant and undesired accessory operations result at a cost and in particular for a continuous microscope testing of routine objects, etc.